Communication system, communication terminal, routing control method, and router

ABSTRACT

A mobile terminal according to the present invention judges, based on a router advertisement transmitted from an access router, whether handover is to be executed between access points connected to the access router, and transmits a link moving notification, which indicates that handover is executed under control of the access router, to the access router. Further, the access router updates only routing information based on the received link moving notification.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/935,265, filed Sep. 8, 2004, and is based upon and claims the benefitof priority from the prior Japanese Patent Application No. 2003-316011,filed on Sep. 8, 2003. The entire contents of these applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a communication system, acommunication terminal, a routing control method, and a router, whichcontrol a packet transfer route.

2. Description of the Related Art

Conventionally, “IP²” (IP-based IMT Network Platform) has been proposedas a routing control method which is applied in the case where acommunication terminal is moved using wireless communication (refer to,for example, T. Okagawa, M. Jo, K. Nishida, and A. Miura, “IP PacketRouting Mechanism Based on Mobility Management in IP-based IMT NetworkPlatform”, International Conference on Intelligence in the nextgeneration Networks (ICIN), 2003, and T. Okagawa et al., “IP PacketRouting Mechanism in IP²”, The Institute of Electronics, Information andCommunication Engineers (IEICE) Technical Report, Mobile MultimediaCommunications (MoMuc) 2002-63, November 2002).

In IP², communication with a mobile communication terminal has beenachieved by using two addresses: a unique host address unique to thecommunication terminal; and a routing host address, which is assigned tothe communication terminal by an access router (edge router) and thelike for routing between routers.

Specifically, as shown in FIG. 1, the access router includes: a routingcache table (RCT) 300 which is a correspondence table between a uniquehost address (IPha) and a routing host address (IPra); a routing table400 having routing information which establishes correspondence betweena unique host address and an output port of an access router; and aneighbor cache 500 holding information which establishes correspondencebetween a MAC address (layer 2 address) and an IP address (layer 3address).

When the communication terminal starts communication through the accessrouter, or executes handover, the access router assigns a routing hostaddress to the communication terminal, that is, the access routerestablishes correspondence between the routing host address and a uniquehost address, and, at the same time, updates the contents of RCT 300 andthe routing table 400.

FIG. 2 shows message procedure for a case where handover is executed forthe communication terminal under control of the access router, that is,between wireless base stations (access points, base stations, and thelike) connected to the same access router. Up on receiving a routeradvertisement which has been transmitted from the access router througha base station of a destination for handover, the communication terminalupdates the neighbor cache created in the communication terminal, andtransmits an activation message, which is a message of an upper layerabove the layer 3, to the access router.

When the access router receives the activation message, the routerre-assigns a routing host address to the communication terminal, andupdates the contents of the routing table 400 which establishescorrespondence between a unique host address and an output port.

The access router transmits an activate notification message to arouting manager, which is a routing management mechanism in a network,in order to register the correspondence between a routing host addressand a unique host address, and updates the contents of RCT 300 accordingto a routing host address update (IPra update) message transmitted fromthe routing manager.

FIG. 3 shows message procedure for a case where the access routertransfers a packet addressed to the communication terminal. As shown inFIG. 3, when the packet addressed to the communication terminal from thenetwork side is received, the access router searches RCT 300 to convertthe routing host address included in the received packet, to a uniquehost address.

The access router then selects a route to the communication terminal,using the routing table 400 based on the converted unique host address,and transmits the packet which has the converted unique host address tothe communication terminal.

However, in IP², when handover is executed between the wireless basestations connected to the same access router for the communicationterminal, re-assignment of the routing host address, updating of therouting table 400, updating of RCT 300 in the access router, andupdating of RCT in the routing manager are executed as described above,though the correspondence between a unique host address and a routinghost address for the communication terminal has been registered in RCT300 of the access router.

Therefore, there has been a problem in that a certain period of time isrequired for completion of the handover for the communication terminaleven when the handover is executed between the wireless base stationsconnected to the same access router.

Further, since the routing information establishing correspondencebetween a unique host address and an output port is registered in therouting table 400, and the amount of information in the routing table400 is increased according to an increase in the number of communicationterminals communicating through the access router, there has been aproblem in that the time required to search for routing information isincreased, and the high-speed transfer of packets becomes difficult inIP². Further, since the access router is required to refer to RCT 300,the routing table 400, and the neighbor cache 500 when the packets aretransferred, there has also been a problem in that the high-speedtransfer of packets becomes difficult.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovecircumstances and its objective is to provide a communication system, acommunication terminal, a routing control method and a router, whichreduces the time required for handover executed between wireless basestations connected to the same access router, and the high-speedtransfer of packets can be realized when a route for packet transfer iscontrolled using a unique host address and a routing host address.

In order to solve the above-described problems, the present inventionhas the following features. A first aspect of the present invention is acommunication system comprising a communication terminal and a router,wherein the communication terminal comprises a judgment unit configuredto judge whether handover is to be executed or not between wireless basestations connected to the router based on a router advertisementtransmitted from the router, and a link moving notification transmitterconfigured to transmit a link moving notification to the router, whichindicates that handover is executed between the wireless base stationsconnected to the router, based on a judgment result by the judgmentunit, and the router comprises a routing information updating unitconfigured to establish correspondence between a unique host addresswhich is unique to the communication terminal and a routing host addressused in the router, and to update a routing information whichestablishes correspondence between the unique host address and an outputport for output of a packet addressed to the communication terminal, andwherein, the routing information updating unit only updates the routinginformation when the link moving notification is received.

According to the above-described aspect, re-assignment of a routing hostaddress and updating of a routing cache table (RCT) can be avoided, anda reduction in the time required for completion of handover can berealized, because only routing information is updated when the routerreceives the link moving notification indicating that the handover isexecuted between the wireless base stations connected with the sameaccess router.

Further, the wasting of network resources is avoided according to thisaspect, because neither the access router nor a routing managertransmits and receives a message to update RCT.

A second aspect of the present invention is a communication terminalcomprising a judgment unit configured to judge whether handover is to beexecuted or not between wireless base stations connected to a routerbased on a router advertisement transmitted from the router and a linkmoving notification transmitter configured to transmit a link movingnotification to the router, which indicates that handover is executedbetween the wireless base stations connected to the router, based on ajudgment result by the judgment unit.

A third aspect of the present invention is a routing control methodwhich is used in a communication system comprising a communicationterminal and a router, having the steps of judging to judge whetherhandover is to be executed or not between wireless base stationsconnected to the router based on a router advertisement transmitted fromthe router, transmitting a link moving notification to the router, whichindicates that handover is executed between the wireless base stationsconnected to the router, based on a judgment result in the judging step,corresponding a unique host address which is unique to the communicationterminal and a routing host address used in the router, updating arouting information which establishes correspondence between the uniquehost address and an output port for output of a packet addressed to thecommunication terminal, and wherein, in the updating step, only therouting information is updated when the link moving notification isreceived.

A fourth aspect of the present invention is a router comprising arouting table storage unit configured to store a routing table whichestablishes correspondence between a routing host address used betweenrouters and an output port for output of a packet addressed to acommunication terminal, an address processor which establishescorrespondence between the routing host address and a unique hostaddress which is unique to the communication terminal, based on therouting table, a route selector which selects the output port, based onthe routing host address included in the packet and the routing table,and an address converter which converts the routing host addressincluded in the packet into the unique host address, based on the resultafter establishing correspondence between the routing address and theunique host address by the address processor.

According to the aspect, the contents of a routing table are not updatedeven if the number of communication terminals which communicate throughthe router is increased. Therefore, an increase in the amount ofinformation in the routing table can be avoided, and a reduction in thetime required to search for routing information can be realized, becausea routing table including a routing information which establishescorrespondence not between the unique host address and output port butbetween the routing host addresses and the output port is used.

In other words, if the routing information establishing correspondencebetween the routing host address assigned to the communication terminaland the output port for a packet is expressed in an integrated manner inthe routing table, for example, the routing information is expressed pernetwork address in the routing table, the amount of the routinginformation in the downward direction, i.e., the routing informationaddressed to the communication terminal can be reduced. Thereby, areduction in the time required for searching for the routinginformation, and the high-speed transfer of packets can be realized.

A fifth aspect of the present invention is a router according to thefourth aspect, wherein the route selector selects the output port, usingan integrated table which establishes correspondence among the routinghost address, the unique host address and the output port, and notifiesthe unique host address of the communication terminal to the addressconverter, and the address converter converts the routing host addressinto the unique host address, based on the notified unique host address.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view showing an example of the contents of a routing cachetable, a routing table, and a neighbor cache, which are used in aconventional router;

FIG. 2 is a view showing message procedure for a case where thecommunication terminal executes handover between wireless base stationsconnected to the same router;

FIG. 3 is a view showing message procedure for a case where aconventional router transfers a packet to a communication terminal;

FIG. 4 is a view showing a network configuration including acommunication terminal and a router according to an embodiment of thepresent invention;

FIG. 5A and FIG. 5B are a view showing configurations of logical blocksfor the communication terminal, and the router according to theembodiment of the present invention;

FIG. 6 is a view showing message procedure for a case where thecommunication terminal executes handover between wireless base stationsconnected to the same router according to a first embodiment of thepresent invention;

FIG. 7 is a view showing message procedure for the communicationterminal, and the router according to a second embodiment of the presentinvention;

FIG. 8 is a view showing an example of the contents of a routing table,a routing cache table (RCT), and a neighbor cache according to thesecond embodiment of the present invention; and

FIG. 9 is a view showing an example of a table into which the routingcache table and the routing table are integrated according to variant ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

A first embodiment of the present invention will now be explained. Inthe first embodiment, an embodiment in which, when a communicationterminal executes handover between wireless base stations connected tothe same router, the communication terminal transmits a link movingnotification that the communication terminal executes handover betweenthe wireless base stations connected to the router, and the routerupdates only routing information, based on the received link movingnotification.

(Network Configuration)

FIG. 4 shows a network configuration including a communication terminaland a router according to the first embodiment. As shown in FIG. 4,access routers AR1 and AR2, which are the router of the embodiment aredeployed in a network 1 which is the network where packets areforwarded. A routing manager RM that is a route management mechanism inthe network 1 is connected to the network 1.

The access router AR1 is connected to access points AP1 and AP2 througha layer-2 switch 10 for switching in the layer 2, using a connectionIF1. The access router AR1 is also connected to an access point AP3using a connection IF2. The access router AR2 is connected to an accesspoint AP4.

The access points AP1 through AP4 are configured to carry out wirelesscommunication with mobile terminals MN1 and MN2 which are thecommunication terminals of the embodiment. For example, a wireless basestation in conformity with a wireless LAN system set forth in theInstitute of Electrical and Electronic Engineers (IEEE) can be used asthe access points AP1 through AP4. Further, the access points AP1through AP4 may be a wireless base station, which carries out wirelesscommunication with cellular telephone terminals.

The mobile terminals MN1 and MN2 are communication terminals having awireless communication function to establish wireless communication withaccess points AP1 through AP4 and, for example, a personal computer, apersonal digital assistant (PDA), a cellular telephone terminal, or thelike can be used as the mobile terminals.

(Configurations of Logical Blocks in Communication Terminal and Router)

The configurations of logical blocks for the communication terminal andthe router of the embodiment will be explained with reference to FIGS.5A and 5B.

As shown in FIGS. 5A and 5B, the mobile terminal MN1 which is thecommunication terminal of the embodiment includes an RA receiver 201, astorage unit 203, a judgment processor 205 and a notification unit 207.Here, the mobile terminal MN2 has the same configuration as that of themobile terminal MN1.

As shown in FIG. 5B, the access router AR1 which is the router of theembodiment comprises, a connection IF1, a connection IF2, a storage unit105, a routing controller 107, an address converter 109, a networkconnection IF111 and a notification receiver 113. Here, the accessrouter AR2 has the same configuration as that of the access router AR1.

The RA receiver 201 is configured to receive a router advertisement (RA)transmitted from the access router AR1. The RA receiving unit 201forwards the received router advertisement to the judgment processor205.

The storage unit 203 is configured to store the contents of a neighborcache that includes information establishing correspondence between aMAC address and an IP address.

The judgment processor 205 is configured to generate an activationmessage to be transmitted to the access router AR1 (access router AR2)to start communication, or to execute handover, up on receiving therouter advertisement forwarded by the RA receiver 201.

In the present embodiment, the judgment processor 205 also forms ajudgment unit which judges, based on the router advertisementtransmitted from the access router AR1 (access router AR2), whetherhandover is to be executed or not between access points (wireless basestations) connected to the same access router.

Specifically, the judgment processor 205 judges whether the routeradvertisement received through an access point under current wirelesscommunication, and the router advertisement received through an accesspoint of a destination for handover have been transmitted from the sameaccess router.

When the router advertisement received through an access point undercurrent wireless communication, and the router advertisement receivedthrough an access point of a destination for handover have beentransmitted from the same access router, the judgment processor 205generates a link moving notification (LMN) which indicates that a linkfor communication is moved under control of the same access router.

Further, the judgment processor 205 updates the contents of the neighborcache stored in the storage unit 203, based on the received routeradvertisement.

The notification unit 207 is configured to transmit the activationmessage generated by the judgment processor 205 to the access router AR1(access router AR2).

In the present embodiment, the notification unit 207 is also configuredto transmit the LMN, which indicates that handover is executed betweenthe access points (wireless base stations) connected to the same accessrouter, to the access router AR1 (access router AR2) based on thejudgment result by the judgment processor 205, and forms a link movingnotification transmitter.

Other than the above-described blocks, the mobile terminal MN1 (mobileterminal MN2) has a block, by which data packets are transmitted andreceived.

Functions of each block of the access router AR1 will now be explained.The connection units IF1 and IF2 are an interface which connects theaccess points and the layer-2 switch 10, and transmits and receivespackets between the units and mobile terminal MN1 (mobile terminal MN2).For example, a LAN interface such as a 100 BASE-TX or the like can beused as the units. Here, the connection units IF1 and IF2 form an outputport which outputs packets addressed to the mobile terminal MN1 (mobileterminal MN2).

The storage unit 105 stores RCT 300, the routing table 400 and theneighbor cache 500 as shown in FIG. 1.

The routing controller 107 is configured to select any one of theconnection IF1, the connection IF2, or the network connection IF111 towhich packets received through the connecting units IF1, IF2, or thenetwork communication IF111 are output, based on the routing table 400stored in the storage unit 105.

The routing controller 107 also updates the contents of the neighborcache 500 based on the received activation message, when it is notifiedfrom the notification receiver 113 that the activation message has beenreceived.

The routing controller 107 assigns a routing host address to the mobileterminal MN1 (mobile terminal MN2), that is, establishes correspondencebetween the unique host address and the routing host address of themobile terminal MN1 (mobile terminal MN2), and transmits an activatenotification message to a routing manager RM to update the contents ofRCT 300 based on an IPra Update message transmitted from the routingmanager RM.

The routing controller 107 then updates the contents of the routingtable 400 based on the unique host address assigned to the mobileterminal MN1 (mobile terminal MN2).

In the present embodiment, the routing controller 107 updates only therouting information on the routing table 400 when the access router AR1receives the link moving notification (LMN) from the mobile terminal MN1(mobile terminal MN2). Here, in the present embodiment, the routingcontroller 107 forms a routing information updating unit.

Specifically, the routing control unit 107 neither assigns a new routinghost address to the mobile terminal MN1 (mobile terminal MN2), norupdates the contents of RCT 300 when it is notified from thenotification receiver 113 that the link moving notification (LMN) hasbeen received.

When it is notified from the notification receiver 113 that the linkmoving notification (LMN) has been received, the routing controller 107updates only the routing information on the routing table 400 becausethe output port of the packet addressed to the mobile terminal MN1 ischanged due to handover executed for the mobile terminal MN1 (mobileterminal MN2) between the access points connected to the access routerAR1.

The address converter 109 is configured to execute conversion betweenthe routing host address included in the packet received through thenetwork connection IF111 and the unique host address. The addressconverter 109 also executes conversion between the unique host addressincluded in the packet received through the connection units IF1/IF2 andthe routing host address.

The network connection IF111 is an interface, by which packets aretransmitted and received between the network connection IF111 and thenetwork 1. For example, a LAN interface such as a 100 BASE-TX or thelike can be used as the network connection IF111.

The notification receiver 113 is configured to receive the activationmessage from the mobile terminal MN1 (mobile terminal MN2), and tonotify the routing controller 107 that the activation message has beenreceived. The notification receiver 113 is also configured to receivethe activate notification message from the routing manager RM, and tonotify the routing controller 107 that the activate notification messagehas been received.

Further, in the embodiment, the notification receiver 113 is configuredto receive the link moving notification (LMN) from the mobile terminalMN1 (mobile terminal MN2), and to notify the routing controller 107 thatthe LMN has been received.

(Routing Control Method Using Communication Terminal and Router)

A routing control method using the communication terminal and the routeraccording to the first embodiment will now be explained.

FIG. 6 shows message procedure for a case in which the mobile terminalMN1 executes handover from the access point AP2 connected to theconnection IF1 of the access router AR1 to the access point AP3connected to the connection IF2 of the access router AR1.

At first, in STEP S10, the mobile terminal MN1 receives a routeradvertisement from the access router AR1 through the access point AP3 ofa destination for handover.

In STEP S20, the mobile terminal MN1 judges, based on the routeradvertisement received in STEP S10 through the access point AP3 and therouter advertisement received through the access point AP2 under currentwireless communication, that handover is executed between the accesspoints connected to the access router AR1.

In STEP S30, the mobile terminal MN1 updates the contents of theneighbor cache, based on the advertisement information received in STEPS10.

In STEP S40, the mobile terminal MN1 transmits the link movingnotification (LMN), which indicates that handover is executed from theaccess point AP2 to the access point AP3, both of which are connected tothe access router AR1, to the access router AR1.

In STEP S50, the access router AR1 updates only the correspondencebetween the unique host address of the mobile terminal MN1 and theoutput port based on the received link moving notification (LMN) in therouting table 400. Accordingly, the access router AR1 neither assigns anew routing host address to the mobile terminal MN1, nor updates thecontents of RCT 300 when the link moving notification (LMN) is received.

Here, the mobile terminal MN1 may transmit the link moving notification(LMN) either by multicast or by unicast. Further, the timing at whichthe mobile terminal MN1 transmits the link moving notification (LMN) tothe access router AR1 may not be the same timing at which the routeradvertisement is received from the access router AR1 through the accesspoint AP3. The timing at which the mobile terminal MN1 transmits the LMNto the access router AR1 may be the timing at which the mobile terminalMN1 switches a radio link to the access router AR1, or to an accesspoint to be connected to the access router AR1.

(Effects)

According to the above-described first embodiment of the presentinvention, re-assignment of a routing host address and updating of arouting cache table (RCT) can be avoided, and a reduction in the timerequired for completion of handover can be realized, because only therouting information is updated when the access router AR1 (access routerAR2) receives the link moving notification indicating that the handoveris executed between the access points connected with the same accessrouter.

Further, the wasting of network resources is avoided according to thefirst embodiment, since neither the access router nor a routing managertransmits and receives a message to update RCT.

Though IP² has been explained as an example in the above-described firstembodiment, the present invention can also be applied to othercommunication methods such as mobile IPv6 (MIPv6). In MIPv6, DAD(Duplicated Address Detection) process is performed when a communicationterminal executes handover. In the DAD process, “care of address (CoA)”is automatically generated based on a router advertisement received froman access router and no duplication of the CoA on a network is confirmedusing multicast.

Further, in MIPv6, control messages (Neighbor Solicitation (NS), andNeighbor Advertisement (NA)) using the multicast are exchanged betweenthe communication terminal and the access router in order to update theneighbor caches in the communication terminal and the access router.

That is, there is a problem being that the network resources are wastedin MIPv6, since the messages using the multicast are exchanged betweenthe communication terminal and the access router. Especially, a measureagainst impersonations of NS and NA is required, because wirelesscommunication is used between the communication terminal and the accessrouter.

Accordingly, the above-described problem can be solved by transmittingthe link moving notification (LMN) using unicast, which indicates thatthe communication terminal executes handover between the access pointsconnected to the same access router, only to the access routerconcerned, as described above.

Second Embodiment

A second embodiment of the present invention will now be explained. Inthe second embodiment, an embodiment in which, a router selects anoutput port for a packet addressed to a communication terminal based onthe routing host address included in the packet using a routing table,which establishes correspondence between a routing host address and anoutput port, and the router converts the routing host address into aunique host address after selecting the output port to transmit thepacket.

Further, in the second embodiment, the router pools a plurality ofrouting host addresses and uses a routing table establishingcorrespondence between pooled routing host addresses and output ports inorder to avoid updating of the contents of the routing table even whenthe communication terminal executes handover.

(Network Configuration and Block Configuration of Router)

In the second embodiment, the same network configuration as that of theabove described first embodiment is used. Further, the logical blockconfiguration of the router of the embodiment is the same as that of theaccess router AR1 explained in the first embodiment.

Here, a block which has different functions from the block of the accessrouter AR1 in the first embodiment will be mainly explained withreference to FIG. 5B.

A storage unit 105 of the present embodiment is configured to store arouting table establishing correspondence between a routing host addressused for the access routers AR1 or AR2 which forms a network 1, and theconnection IF1 (or, connection IF2) which outputs packets addressed tothe mobile terminal. The storage unit 105 of the present embodimentforms a routing table storage unit.

Specifically, the routing table, in which the contents are differentfrom the conventional ones shown in FIG. 1, and a routing cache tableare stored in the storage unit 105. Here, FIG. 8 shows an example of thecontents of a routing cache table (RCT) 310, a routing table 410, and aneighbor cache 500, which are stored in the storage unit 105 of theaccess router AR1 according to the present embodiment. As shown in FIG.8, the routing table 410 establishes correspondence between the routinghost addresses and the output ports, not between the unique hostaddresses and the output port.

In the present embodiment, the routing controller 107 forms an addressprocessor which establishes correspondence between the routing hostaddresses and the unique host address of the mobile terminal MN1 (mobileterminal MN2) based on the routing table 410.

Specifically, the routing table 410 includes a routing informationestablishing correspondence between a plurality of routing hostaddresses (P1_ra through P4_ra) pooled in the access router AR1 and theoutput ports (connection IF1 or connection IF2), as shown in FIG. 8.

Here, the pooled host addresses for routing may be expressed, forexample, per network addresses in the routing table 410. The accessrouter AR1 may decide the routing host address assigned to the mobileterminal MN1 (mobile terminal MN2) based on the routing table 410expressed by the network address.

For example, when the routing host address is assigned to the mobileterminal MN1, the routing controller 107 assigns the pooled routing hostaddress to the mobile terminal MN1, based on the output port (connectionIF1 or IF2), which is connected with an access point where the mobileterminal MN1 establishes wireless communication, and the routing table410.

More specifically, for example, in the case where wireless communicationis established by the mobile terminal MN1 through the access point AP2,the access router AR1 refers to the routing table 410, and the routinghost address (P1_ra) in correspondence with the output port (connectionIF1), to which the access point AP2 is connected, is assigned to themobile terminal MN1 by the access router AR1.

The routing controller 107 then establishes correspondence between theunique host address (MN1_ha) of the mobile terminal MN1 and the routinghost address (P1_ra) as shown in RCT 310. The routing controller 107then transmits an activate notification message to a routing manager RMand updates the contents of RCT 310, based on a IPra Update messagetransmitted from the routing manager RM.

In the present embodiment, the routing controller 107 forms a routeselector in which the output port (connection IF1 or connection IF2) isselected, based on the routing host address included in the packetaddressed to the mobile terminal MN1 (mobile terminal MN2) and therouting table 410.

For example, the routing controller 107 selects the output port(connection IF1), based on the routing host address (P1_ra) included inthe packet addressed to the mobile terminal MN1 and the routing table410 as shown in FIG. 8. Then, based on RCT 310, the routing controller107 acquires the unique host address (MN1_ha) of the mobile terminal MN1in correspondence with the routing host address (P1_ra) included in thepacket addressed to the mobile terminal MN1.

Further, the routing controller 107 transmits the packet addressed tothe mobile terminal MN1 which has been converted into the unique hostaddress (MN1_ha) by the address converter 109 to the mobile terminalMN1, referring to the contents of the neighbor cache 500.

In the present embodiment, the address converter 109 converts therouting host address into the unique host address as a result ofcorrespondence between the routing host address and the unique hostaddress by the routing controller 107, that is, based on the contents ofRCT 310.

Here, in the above-described second embodiment, the transmitted packetaddressed to the network 1 from the mobile terminal MN1 (mobile terminalMN2), is converted from the unique host address into the routing hostaddress in the address converter 109, based on RCT 310. The routingcontroller 107 then transmits the packet to the network 1 through anetwork connection IF111, based on the converted routing host address.

(Routing Control Method Using Router)

A routing control method using a router according to the secondembodiment will now be explained with reference to FIG. 7. Here, themobile terminal MN1 starts communication through the access point AP2 asshown in FIG. 4.

At first, in STEP S110 the mobile terminal MN1 receives a routeradvertisement transmitted from the access router AR1 through the accesspoint AP2 as shown in FIG. 7.

In STEP S120, the mobile terminal MN1 updates the contents of theneighbor cache, based on the router advertisement received in STEP S110.

In STEP S130, the mobile terminal MN1 transmits an activation message tothe access router AR1 for communication through the access router AR1.

In STEP S140, the access router AR1 assigns the routing host address(for example, P1_ra) to the mobile terminal MN1, and establishescorrespondence between the routing host address (P1_ra) and the uniquehost address (MN1_ha) of the mobile terminal MN1, based on the routingtable 410, and that the mobile terminal MN1 establishes communicationthrough the access point AP2, that is, communication is established bythe mobile terminal MN1 through the connection IF1.

In STEP S150, the access router AR1 transmits the activate notificationmessage to the routing manager RM.

In STEP S160, the routing manager RM establishes correspondence betweenthe unique host address (MN1_ha) to the mobile terminal MN1 and therouting host address (P1_ra), based on the received activatenotification message, and updates the contents of the routing cachetable (RCT).

In STEP S170, the routing manager RM transmits the IPra update messageto the access router AR1.

In STEP S180, the access router AR1 updates the contents of RCT 310,based on the received IPra update message in order to reflect thecorrespondence between the routing host address (P1_ra) transmitted inSTEP S150 and the unique host address (MN1_ha) of the mobile terminalMN1.

Next, message procedure in which the access router AR1 receives thepacket addressed to the mobile terminal MN1, and transmits the packet tothe mobile terminal MN1 will be explained.

In STEP S210, the access router AR1 receives the packet addressed to themobile terminal MN1 through the network 1.

Based on the routing host address (P1_ra) included in the receivedpacket addressed to the mobile terminal MN1, in STEP S220, the accessrouter AR1 searches for the routing table 410, and selects the outputport (connection IF1) through which the packet is output.

In STEP S230, the access router AR1 searches RCT 310, based on therouting host address (P1_ra) included in the received packet addressedto the mobile terminal MN1, to acquire the unique host address (MN1_ha)of the mobile terminal MN1.

In STEP S240, the access router AR1 converts the routing host address(P1_ra) included in the packet addressed to the mobile terminal MN1 intothe unique host address (MN1_ha) of the mobile terminal MN1.

In STEP S250, the access router AR1 transmits the packet that wasaddressed to the mobile terminal MN1, and has been converted into theunique host address (MN1_ha) of the mobile terminal MN1, referring tothe neighbor cache 500, to the mobile terminal MN1.

(Effects)

According to the above-described second embodiment of the presentinvention, the contents of the routing table 410 are not updated even ifthe number of mobile terminals which communicate through the accessrouter AR1 (access router AR2) is increased, an increase in the amountof information in the routing table 410 can be avoided, and a reductionin the time required for searching for the routing information can berealized, because correspondence between the routing host address andthe unique host address is established, using the routing table 410including the routing information which establishes correspondence notbetween the unique host address and the output port, but between therouting host address and the output port.

That is, if the routing information establishing correspondence betweenthe routing host address assigned to the mobile terminal MN1, MN2 andthe output port (connection IF1 or IF2) of the packet is expressed in anintegrated manner in the routing table 410, for example, if the routinginformation is expressed per network address, the amount of the routinginformation in the downward direction, that is, the amount of routinginformation addressed to the mobile terminal MN1 and the mobile terminalMN2 can be reduced. Thereby, a reduction in the time required forsearching for routing information, and the high-speed transfer ofpackets can be realized.

[Variant]

Though the routing cache table (RCT) and the routing table have beenseparately provided in the above-described first and second embodiments,a table in which the routing cache table (RCT) and the routing table areintegrated together can be used.

For example, if there is correspondence established among a unique hostaddress (IPha), a routing host address (IPra) and an output port(connection IF1 or connection IF2) as shown in FIG. 9, theabove-described first and second embodiments can be realized by using anaccess router having an integrated table 600.

For example, when the access router AR1 uses the integrated table 600 inthe above-described second embodiment, the routing controller 107selects an output port by using the integrated table 600, and at thesame time, notifies a unique host address (MN1_ha) of the mobileterminal MN1 to the address converter 109. Further, the addressconverter 109 converts a routing host address included in a packetaddressed to the mobile terminal MN1 into the unique host address(MN1_ha), based on the notified unique host address (MN1_ha).

That is, further high-speed transfer of packets can be achieved, sincethe access router AR1 can search the correspondence among routinginformation, host addresses for routing, and unique host addresses oneat a time, using the integrated table 600.

According to the present invention, there can be provided communicationsystem, a communication terminal, a routing control method and a router,which reduces the time required for handover executed between wirelessbase stations connected to the same access router, and the high-speedtransfer of packets can be realized when a route for packet transfer iscontrolled using a unique host address and a routing host address.

1. A communication terminal comprising: a judgment unit to judge whethertwo router advertisements are transmitted from a same router ordifferent routers; and a link moving notification transmitter totransmit a link moving notification to the router, which indicates thathandover is executed between the wireless base stations connected to thesame router, when it is judged that the two router advertisements aretransmitted from the same router.
 2. The communication terminalaccording to claim 1, wherein the judgment unit is to judge whether thetwo router advertisements are transmitted from the same router or thedifferent routers based on a first router advertisement received througha wireless base station under current wireless communication and asecond router advertisement received through a wireless base station ofa destination for handover.
 3. A router comprising: a notificationreceiver to receive a link moving notification from a communicationterminal, the link moving notification indicates that handover isexecuted between wireless base stations connected to the router; and arouting information updating unit to update a routing information, whichestablishes correspondence between a unique host address which is uniqueto the communication terminal and a routing host address used in therouter and establishes correspondence between the unique host addressand an output port for output of a packet addressed to the communicationterminal, according to the handover of the communication terminal,wherein the routing information updating unit is to only update thecorrespondence between the unique host address and the output port whenthe link moving notification is received.
 4. The router according toclaim 3, further comprising: an address converter to convert the routinghost address into the unique host address and convert the unique hostaddress into the routing host address, by using an integrated tablewhich establishes correspondence among the routing host address, theunique host address and the output port.